System and Method for Installing Foundation Elements

ABSTRACT

The invention pertains to a system ( 1 ) for installing foundation elements, such as piles or conductors ( 2 ), in a sub-sea ground formation ( 3 ), comprising a hydraulic driver ( 8 ) and a power converter ( 9 ) for generating hydraulic pressure in a hydraulic fluid for the driver ( 8 ). The driver ( 8 ) and the converter ( 9 ) are adapted to fit inside the foundation elements ( 2 ).

The invention pertains to a system for installing foundation elements, such as piles or conductors, in a sub-sea ground formation, comprising a hydraulic driver and a power converter for generating hydraulic pressure in a hydraulic fluid for the driver. The invention also relates to a method of installing foundation elements.

U.S. Pat. No. 4,964,473 relates to a method for driving a hydraulic submerged tool, whereby the hydraulic pressure energy is generated in a submerged power converter. As explained in U.S. Pat. No. 4,964,473, such a method was already known in the art, i.e. from the Netherlands patent application Nr. 7513240, which corresponds to U.S. Pat. No. 4,043,405.

The latter document discloses a hydraulically driven pile driver to which an electrically driven hydraulic power unit is attached in which electric power is converted into hydraulic power. Feeding this power converter occurs by supplying electric energy by electric cables to the power converter from a generator located above water ashore, or on a ship or on a work platform. In the same way other submerged tools are driven, such as drilling tools, sampling apparatuses and tools for working at or inspecting submarine constructions.

The electrical cables are uncoiled from a reel on deck to follow the power converter lowered below the water. For work ships with their restricted deck space and hoisting capacity suchlike reels with cables and diesel-electric power units are very aggravating.

Further, with an increase of the depth on which has to be worked, extension of the electric cables is almost impossible or very complicated, because in most cases these are combined cables for electrical power, electrical signals and air supply. These cables moreover are rather heavy, costly and vulnerable.

The invention underlying U.S. Pat. No. 4,964,473 aims to provide a method as well as a device for driving a hydraulic submerged tool with which these problems can be solved in an easy way. According to U.S. Pat. No. 4,964,473, this object is obtained by driving the converter with pressurised surrounding water, which, after the energy transfer, is exhausted into the surrounding water. Herewith a simple drive is obtained whereby no return conduct is necessary. Especially with drilling ships in which high-pressure sea water pumps are already present and in which the drilling pipe composed of sections also can be used for transporting the pressurised sea water, this method will give a considerable cost reduction, whereas the working depth may be very large.

It is an object of the present invention to improve the system according to the opening paragraph.

To this end, the system according to the present invention is characterised in that the driver and the converter are adapted to fit inside the foundation elements.

This system enables so-called “pile toe driving” without the need for an umbilical between the converter and the driver.

Typically, hydraulic pile drivers are connected to a tank for a hydraulic fluid and comprise a hydraulic cylinder, a piston accommodated in the hydraulic cylinder, an impact weight connected to the piston, high and low-pressure accumulators, a valve system for alternately connecting the hydraulic cylinder to the high and low-pressure accumulators, and conduits for operatively connecting these components in a manner known in itself.

It is preferred that the tank is mounted on or integrated with the converter. It is also preferred that the cylinder, piston, accumulators, and the valve system are mounted on or integrated with the converter to form a converter drive unit.

By integrating one or more components of the driver with the converter, preferably most or all components except for the impact weight, handling of the system is simplified, a housing for the weight may be omitted and/or tolerances and shape of the weight become less critical.

To further separate the weight from the converter drive unit, it is preferred that the weight is connected to the piston by means of a flexible element, such as a cable, chain or telescopic member, and preferably a shock absorber.

The invention further relates to a method of installing hollow foundation elements, such as piles or conductors, in a sub-sea ground formation, by means of a hydraulic driver and a power converter for generating hydraulic pressure in a hydraulic fluid for the driver, which method comprises the steps of (in no particular order)

mounting the driver inside a foundation element and, typically subsequently, mounting the converter inside the foundation element, and

lowering the foundation element, the driver, and the power converter from a vessel, such as an drilling platform or ship, preferably by means of a drill string.

It is preferred that an energy transferring fluid, in particular water taken from the surroundings of the drilling platform or ship, is fed to the converter through the drill string.

It is noted that WO 2004/051004 discloses a “pile-driving apparatus comprising a pile, a shoe tip coupled to a toe of the pile, and a drill string disposed within the pile. The drill string comprises a gripping device coupling the drill string to the pile and a hammer deployed into the pile such that the hammer is capable of transmitting a force to the shoe tip.” The hammer receives fluid to generate the force, used to drive the shoe tip, and controlling signals via an umbilical.

Further, U.S. Pat. No. 6,626,248 discloses a “method for driving a drive pipe into a sub-sea formation, said method comprising: accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; transferring energy from the accelerated at least one mass to the drive pipe; suspending the drive pipe from a drill string; and isolating [by means of a “running tool”] the drill string from the transferred energy from the accelerated at least one mass.”

The invention will now be explained in more detail with reference to the figures, which show a preferred embodiment of the system according to the present invention.

FIG. 1 schematically shows a system according to the present invention suspended from drilling platform by means of a drill string.

FIG. 2 is an enlarged view of the system shown in FIG. 1.

It is noted that the drawings are not necessarily to scale and that details, which are not required for understanding the present invention, may have been omitted.

The Figures show a system 1 for installing foundation elements, such as tubular piles or conductors 2, in a seabed 3, suspended from a drilling platform 4 by means of a cable, a reinforced umbilical or, preferably, a drill string 5.

In this example, the foundation element is a so-called conductor pipe 2, i.e. a hollow metal tube, which typically has a length in a range from 50 to 125 m or even up to 250 m (in deep water) and a diameter in a range from 70 to 100 cm, for instance 30 or 36 inch. Near its bottom, the conductor pipe 2 is provided with a drive shoe 6 and a toe drive assembly, a steel plate or a solid steel anvil 7.

The system 1 comprises a hydraulic driver 8 and a power converter 9 for generating hydraulic pressure in a hydraulic fluid and supplying the same to the driver 8, which both fit inside the conductor pipe 2.

The driver 8 comprises a tank 10 for hydraulic fluid, such as hydraulic oil or (sea)water optionally including appropriate additives, a hydraulic cylinder 11, a piston 12 reciprocatingly accommodated in the hydraulic cylinder 11, high and low-pressure accumulators 13, 14, a valve system 15 for alternately connecting the hydraulic cylinder 11 to the high and low-pressure accumulators 13, 14, a volume compensator (not shown), typically a piston compensator, for compensating fluctuations of the volume of hydraulic fluid in the tank 10 (resulting from the movements of the piston 12), and an impact weight 17. Further, an acceleration chamber 16 is positioned above the piston 12 and connected to the valve system 15.

In accordance with a preferred aspect of the present invention, the impact weight 17 has been separated from the other components 10-15 of the driver 8 and has been adapted to reciprocate inside the conductor pipe 2. The impact weight 17 comprises a plurality of guides 18, preferably mounted along the circumference of the impact weight 17 and at least at or near its upper and lower ends. The guides 18 abut the inner wall of the foundation element 2 and are preferably made of a synthetic material, such as HDPE, or a metal, such as brass. The guides 18 eliminate nearly all wear on the impact weight 17 and allow the weight 17 to work at inclinations.

The impact weight 17 is connected to the lower end of the piston 12 by means of a flexible element 19, e.g. a steel cable, and a shock absorber 20.

The converter 9 is preferably a fluid pressure converter comprising a so-called mud motor 21, a fluid inlet 22, connected to the drill string 5, such that a fluid, in particular seawater taken from the surroundings of the drilling platform 4, can be fed through the drill string 5 to the converter 9, and a pump 23 connected to the high-pressure accumulator 13 and the valve system 15. Further, conduits 24, 25 are provided to connect the low-pressure accumulator 14 to the tank 10 and the pump 23 to the tank 10 and the high-pressure accumulator 13, respectively.

The mud motor 21, e.g. a Moyno 962M3460 or a 212RS625 ex Roper pumps, is known in itself and comprises a power section, connected, via the fluid inlet 22, to the drill string 5, a transmission, and an output shaft connected to the pump 23.

In an alternative embodiment (not shown), mostly suitable for foundation elements having a large diameter, the converter comprises one or more work cylinders, which each by means of a floating piston are divided in a space filled with pressurised water and a space filled with a hydraulic work medium, switching means being provided which are activated each time that a floating piston reaches the end of its work stroke, by reason of which at each work cylinder the space which can be filled with pressurised water alternately is connected either to a feed conduit of pressurised water, in particular the drill string 5, or to a free exhaust (not shown), each work cylinder at the side of the hydraulic work medium being connected to the pressure conduit 25 running to the high-pressure accumulator 13. With this relatively simple device, a practically loss free energy conversion is realized. Further details on this type of converter can be found in U.S. Pat. No. 4,964,473, which is incorporated herein by reference.

In the preferred embodiment shown in the Figures, the tank, cylinder, piston, accumulators, and valve system have been integrated with the converter to form a converter driver unit 26. An expandable ring, for instance a so-called packer 27, or a gripper has been attached about the circumference of the unit 26, e.g. halfway or at both the upper and lower ends of the unit 26, to temporarily secure the unit 26 to the inner wall of the foundation element 2. Optionally, the ring 27 and the anvil 7 provide air tight seals, in which case water below the unit 26 can be replaced by e.g. air thus reducing the resistance on the impact weight 17 during reciprocating movement inside the foundation element 2.

The conductor pipe 2 is installed in the seabed 3, by lowering the conductor pipe 2 from the platform 4 into the sea, mounting the impact weight 17 and the converter driver unit 26 inside the pipe 2, attaching the converter driver unit to the drill string, securing the latter against the inner wall of the pipe 2, e.g. by expanding the ring 27 and/or connecting the pipe 2 to the drill string 5 by means of (W)ROV disconnectable slings, lowering the assembly thus obtained from the drilling platform 4 by means of the drill string 5, and positioning the conductor pipe 2 on the seabed 3.

The operating cycle begins with an upward movement involving the lifting of the piston 12 and the impact weight 17. A first valve (within the valve system 15) in the high-pressure line (25) is opened and a second valve in the return line (24) is closed. Once a preset stroke has been reached, the first valve is closed and the second valve opened, allowing the impact weight 17 to start its downward movement. In this example, the flexible element 19 is sufficiently short to enable the piston 12 to abut and hence accelerate the impact weight 17 during downward movement by connecting the chamber 16 above the piston 12 to the high-pressure line, giving the impact weight 17 a total acceleration of up to 2 g. This reduces the actual stroke required and increases the blow rate. At impact the weight strikes the anvil 7 and the pipe 2 is driven into the seabed 3.

From the above examples, it will be clear that system according to the invention enables so-called “pile toe driving” without the need for an umbilical between the converter and the driver. Further, by integrating one or more components of the driver with the converter, preferably most or all components except for the impact weight, handling of the system is simplified, a housing for the weight may be omitted and/or tolerances and shape of the weight become less critical.

The invention is not restricted to the above-described embodiments, which can be varied in a number of ways within the scope of the claims. For instance, the impact weight (17) may be rigidly connected to the piston (12). The means (27) for securing the converter driver unit to the inner wall of the foundation element can be employed to absorb torque generated in the converter, thus reducing or even preventing torque in the drill string.

Also, the converter may comprise two or more pumps, e.g. two main pumps driven in opposite directions (again, reducing torque) and a pump for driving a jet for removing obstacles in the way of the impact weight.

Further, the converter and driver can be configured as separate units, preferably connected by a flexible element and suitable conduits for the hydraulic fluid and/or each provided with a means for securing the same to the inner wall of the foundation element. 

1. System (1) for installing foundation elements, such as piles or conductors (2), in a sub-sea ground formation (3), comprising a hydraulic driver (8) and a power converter (9) for generating hydraulic pressure in a hydraulic fluid for the driver (8), characterised in that the driver (8) and the converter (9) are adapted to fit inside the foundation elements (2).
 2. System (1) according to claim 1, comprising a tank (10) for a hydraulic fluid, which tank (10) is mounted on or integrated with the converter (9).
 3. System (1) according to claim 1 or 2, comprising a hydraulic cylinder (11), a piston (12) accommodated in the hydraulic cylinder (11), high and low-pressure accumulators (13, 14), and a valve system (15) for alternately connecting the hydraulic cylinder (11) to the high and low-pressure accumulators (13, 14), wherein the cylinder (11), piston (12), accumulators (13, 14), and valve system (15) are mounted on or integrated with the converter (9; 26).
 4. System (1) according to any one of the preceding claims, comprising an impact weight (17) adapted to reciprocate inside a foundation element (2) and preferably to abut the inner wall of the foundation element (2), which impact weight (17) is connected to the piston (11) by means of a flexible element (19).
 5. System (1) according to any one of the preceding claims, comprising an acceleration compartment located above the piston (11) and/or communicating with a chamber (16) above the piston (11).
 6. System (1) according to any one of the preceding claims, wherein the driver (8) and/or the converter (9; 26) comprises a means for securing the driver (8) and/or the converter (9; 16) and any components integrated therewith to the inner wall of the foundation element (2).
 7. System (1) according to any one of the preceding claims, wherein the converter (9; 26), preferably a fluid pressure converter, comprises a fluid inlet adapted to be connected to a drill string (5), such that a fluid can be fed through the drill string (5) to the converter (9; 26).
 8. Method of installing hollow foundation elements, such as piles or conductors (2), in a sub-sea ground formation (3), by means of a hydraulic driver (8) and a power converter (9) for generating hydraulic pressure in a hydraulic fluid for the driver (8), which method comprises the steps of mounting the driver (8) and the converter (9; 26) inside the foundation element (2), lowering the foundation element (2), the driver (8), and the power converter (9) from a vessel (4).
 9. Method according to claim 8, wherein the converter (9; 26) and any components integrated therewith is lowered by means of a drill string (5).
 10. Method according to claim 9, wherein an energy transferring fluid is fed to the converter (9; 26) through the drill string (5).
 11. Method according to any one of claims 8-10, wherein the driver (8) and the power converter (9) are positioned and preferably secured inside the foundation element (2) before lowering the foundation element (2), the driver (8), and the power converter (9) to the formation (3).
 12. Method according to any one of claims 8-11, wherein the converter (9; 26) and elements integrated therewith are secured to the inner wall of the foundation element (2).
 13. Method according to any one of claims 8-12, wherein water below the converter (9; 26) is replaced by a gas, thus reducing the resistance on the impact weight (17) during reciprocating movement inside the foundation element (2).
 14. Method according to any one of claims 8-13, wherein the impact weight (17), during reciprocating movement, is guided by the inner wall of the foundation element (2). 